242 



AGRONOMY 



mixture, and continue boiling for about half an hour. Five 

 or ten pounds of salt is often added while boiling. This 

 mixture does not keep and should be used as soon as made. 

 The wash may also be made by taking double the quantity 

 of lime, slaking it with boiling water, and adding the sulphur 

 while still hot; or the heat developed by the lime in .slaking 

 may be sufficient. This latter is called the unboiled wash. 



FIG. 179. Potato field attacked by late blight, showing the difference 

 between sprayed and unsprayed rows 



From Duggar's " Fungous Diseases of Plants " 



Ammoniacal copper carbonate. This spray is made by add- 

 ing five ounces of copper carbonate and three pints of am- 

 monia to about fifty gallons of water. A paste is first made 

 with the copper carbonate and a little water, the ammonia is 

 added, and then the rest of the water. The mixture should 

 stand until it settles, and only the clear liquid on top should 

 be used. This spray is effective against rusts, leaf spots, and 

 blights. 



